Conceptual Site Models

Our suc­cess as en­vi­ron­men­tal pro­fes­sion­als often re­quires mak­ing sense of com­plex sci­en­tific data sets at our sites to a diverse audience that may include risk assessors, earth scientists, remediation engineers, regulators and the public. The CSM provides a "picture" of the physical, chemical and biological processes that influence the transport, migration and potential impacts of contamination from its sources through environmental media to receptors within the environmental system. Conceptual site models help stakeholders visualise these complex interactions and create a common understanding for decisions and actions.

Dynamic Models Evolve with Re­me­di­a­tion Progress

CSM are not static, and should never be con­sid­ered totally accurate or “complete”; instead, they should be viewed as dynamic and evolving as the re­me­di­a­tion process pro­gresses and new data are col­lected. They have a dif­fer­ent role in each phase of a re­me­di­a­tion project from pre­lim­i­nary in­ves­ti­ga­tion through remedial action (often over­looked) and post-cleanup mon­i­tor­ing:

• Pre­lim­i­nary – Initiate an in­ves­ti­ga­tion.
• Baseline – Guide the in­ves­ti­ga­tion based on sys­tem­atic planning.​Char­ac­ter­i­za­tion – Dictate any needed modi­fi­ca­tions to address important data gaps by incor­po­rat­ing new in­for­ma­tion through it­er­a­tive updates as the in­ves­ti­ga­tion proceeds.
• Remedy se­lec­tion and design – Form the basis of the fea­si­bil­ity study and remedial design.
• Re­me­di­a­tion and post-remedial action mon­i­tor­ing – Provide a means to optimise (or modify) the remedy through it­er­a­tive updates as per­for­mance mon­i­tor­ing data are col­lected.

Because we cannot “see” into the ground or char­ac­ter­ise every aspect of a site, CSM will always be based on as­sump­tions and in­ter­pre­ta­tions. We must balance the degree of un­cer­tainty with current decision needs. A key decision point in the life of a re­me­di­a­tion project is deciding when the in­ves­ti­ga­tion phase is done and the CSM is suf­fi­ciently complete to identify and select ap­pro­pri­ate remedies. From a risk as­sess­ment stand­point, this usually means po­ten­tial mi­gra­tion pathways are eval­u­ated and exposure point con­cen­tra­tions ad­e­quately quan­ti­fied. From a con­t­a­m­i­nant dis­tri­b­u­tion stand­point, this usually means de­lin­eation of the nature (con­t­a­m­i­nants and con­cen­tra­tions) and extent. However, often over­looked until too late in the char­ac­ter­i­sa­tion stage are many of the hy­dro­ge­o­log­i­cal and bio­geo­chem­i­cal at­trib­utes of a site that in­flu­ence the se­lec­tion of po­ten­tial remedial tech­nolo­gies, cost es­ti­mat­ing and the remedial design. Ac­cord­ingly, a critical stage in the de­vel­op­ment of a robust CSM is the iden­ti­fi­ca­tion of data needs of all parties involved in the se­lec­tion and design of the remedial so­lu­tions.

As sites and con­cep­tual site models become more complex, CDM Smith has found that ge­o­graphic in­for­ma­tion systems (GIS), ef­fec­tive data man­age­ment and vi­su­al­isa­tion tools greatly fa­cil­i­tate the func­tion­al­ity of the CSM. GIS-based CSM are es­pe­cially well suited for en­vi­ron­men­tal site char­ac­ter­i­sa­tion and re­me­di­a­tion because they are a means to compile, vi­su­al­ise, compare and analyse lots of spa­tially related data, bringing the many pieces of the puzzle together. This also fa­cil­i­tates nearly au­to­mated CSM updates through addition of newly col­lected data to the database. In addition, they enable remedy eval­u­a­tions by allowing the en­vi­ron­men­tal pro­fes­sional to quickly cal­cu­late nu­mer­i­cal and area-weighted average con­cen­tra­tions, graph­i­cally select data sets to assess re­me­di­a­tion volumes, evaluate residual con­cen­tra­tions, and target specific regions and geologic strata for po­ten­tial remedies. Reg­u­la­tory in­ter­ac­tions re­gard­ing the adequacy of site char­ac­ter­i­sa­tion and re­al­is­tic remedy se­lec­tion are enhanced because all the data are visually in­te­grated and at your fin­ger­tips for real-time ma­nip­u­la­tion. Finally, GIS-based CSM greatly fa­cil­i­tate report prepa­ra­tion and enhance com­mu­ni­ca­tions with stake­hold­ers and the public.